Method of making a vapor device



, Jan. 7, 1969 w. B. HALL METHOD OF MAKING A VAPOR DEVICE Filed OGt. 27,1966 United States Patent O 3,419,950 METHOD F MAKING A VAPOR DEVICEWilliam B. Hall, Lancaster, Pa., assigner to Radio Corporation ofAmerica, a corporation of Delaware Filed Oct. 27, 1966, Ser. No. 589,987U.S. Cl. 29-422 Int. Cl. B23p I7/ 00 My invention relates to a method ofmaking a vapor device and particularly to a method of evacuating andsealing such devices.

One type of vapor device is a heat pipe which is used to convey heatfrom a heat source such as a fossil fuel ame, to a heat utilization ordissipation zone. A heat pipe usually comprises a tubular structurehaving a capillary lining and a vaporizable heat transfer or workingmedium therein. The vaporizable Working medium is selected to have avaporization temperature at least as high as the operating temperatureof the heat pipe. When such operating temperature is about 1400 C.,lithium may be used as the working medium.

For most ellicient operation of the heat pipe it is desirable that theenvelope of the heat pipe as well as the working medium be evacuated ofsubstantially all undesirable foreign gases. Gases Within the envelopeof the device adversely affect efficiency by collecting in regions wherethey form insulating barriers to the vapor transport of heat. When suchgas collecting regions are formed adjacent to the envelope wall at theheat input zone, the heat input to the heat pipe from the heat source isreduced. When the gases collect on the envelope wall at the heatutilization or dissipation zone, the heat output of the pipe islessened.

When a heat pipe is designed for operating at a relatively hightemperature of about 1400 C., for example, it is desirable for maximumgas evacuation that the heat pipe envelope as Well as the Working mediumbe heated to a temperature that is higher than the operating temperatureduring the evacuating step, and that the envelope be sealed before thetemperature is lowered. In this Way, evolution of gases from theenvelope walls and from the working medium that would normally takeplace during operation, is avoided and longer high eiciency operation ofthe heat pipe is assured. It is also desirable to compensate for loss ofWorking medium during the outgassing and evacuating step.

After the device envelope has been evacuated of undesired gases, it isdesirable to seal the envelope while at the aforementioned highertemperature and while connected to an exhaust system.

Accordingly, it is an object of the invention to outgas the walls of theenvelope of a vapor device as well as the working medium therein, at atemperature at least as high as the intended operating temperature ofthe device while preserving an amount of working medium in the devicerequired for efficient operation of the device.

Another object is to hermetically seal the device envelope in aconvenient manner after gases therein, including gases evolved duringthe outgassing step, have been evacuated.

In carrying out a preferred embodiment of my novel method, a device,e.g., a heat pipe with a working medium therein is heated at least toits intended temperature of operation. This temperature serves to outgasthe heat pipe envelope and the working medium therein. While at suchtemperature, the heat pipe envelope is evacuated to a reduced pressurewhich may be about -6 torr. The evacuation is preferably effectedthrough an elongated passageway terminating in an orifice in one end ofthe heat pipe envelope. A wire or rod of such diameter as to nearlyclose the orifice may be positioned in the passageway. To preventcondensation of the working medium in the re- 10 Claims ICC gion of theorifice, the passageway walls as well as the wire, are heated to atemperature higher than the temperature of operation of the device. Thelength of the passageway helps to control the flow of Working mediumtherethrough as a consequence of frictional losses therein.

During the outgassing operation, some loss of the working medium isunavoidable. I have provided a preferred Way for determining themagnitude of the relatively small amount of Working medium lost duringthe outgassing and evacuating step. l initially provide an excess amountof the Working medium in the heat pipe and when this amount has beenlost I seal the envelope so that an optimum quantity of working mediumremains in the heat pipe after the evacuating and sealing steps havebeen completed.

Further objects and features of my novel method will become apparent asthe present description continues.

In the drawing, to which reference is now made for an illustrativeexample of my novel method:

FIG. l is a sectional view of a heat pipe associated with apparatus foroutgassing, evacuating and hermetically closing the envelope thereof;and

FIG. 2 is a fragmentary sectional View, partly schematic, of means fordetermining the amount of working medium lost during a practice of mymethod.

In practicing my novel method, as shown in FIG. 1, a heat pipe 10 havingan envelope 11 and a capillary lining 12 is provided with a desiredquantity of working medium 13 such as lithium. The wall of envelope 11has a thickness of about 0.030 inch in one example. At one end of theenvelope 11 is a reduced area extension or nipple 14 dening an elongatedpassageway terminating in an orice 16. The envelope 11 and the nipple 14may be made of a refractory metal such as molybdenum. The capillarylining 12 may be made of a molybdenum wire mesh having capillaryopenings.

A wire or rod 18 has a thinned-down portion 19 extending into theorifice 16. The Wire portion 19 has a cross sectional area for nearlyclosing the orice 16. The wire 18 including portion 19 is made of ametal having a higher melting point temperature than the Walls of theorice 16. Where the passageway walls are made of molybdenum having amelting point temperature of 2620 C. the Wire 18 may be made of tungstenhaving a melting point temperature of 3370 C. In this Way the wire 18prevents collapse of the nipple when the walls thereof are heated to asealing temperature.

In one example, the portion 19 of wire 18 lhas a diameter of about 0.060inch while orifice 16 has a diameter of about 0.062 inch. This providesan 0.001 inch annular space around the wire portion ,19. The wallthickness of the nipple is about 0.04 inch and its length is about 0.5lmil. This Wall thickness is signicant in that it is sufliciently smallto avoid the formation of an undesirably large heat sink in the nippleand provides desired resistance for heating by 12R losses. Heat-retaining capacity of the nipple heat sink is increased with increasein the mass of the nipple 14. If the heat sink is large enough it maydraw heat away from the inner surface region of the orifice to such adegree that the wire portion 19 will melt before the inner surfaceregion melts. Such melting of the wire 19 is objectionable in that itmay not result in the formation of a desired closing meniscus.

ln practicing my method, the heat pipe 10 is supported within a bell jar20 Where the heating of the heat pipe 10 is accomplished by electriccurrent losses therein. The heat pipe may be supported on an insulatingdisc 22, made of ceramic for example and hermetically sealed to a base24 upon which the bell jar 20 rests and to which it is hermeticallysealed. The bell jar 20 is evacuated to a pressure of about 10-6 torrthrough an exhaust tubul'ation 26.

The heat pipe has a heat input region 28 which may be heatedelectrically by 12R losses as by a transformer 3i) connected to asuitable electrical power supply, not shown. The heat input region 28may be heated to the operating temperature, i.e., about 1400 C. by apower input thereto of 2500 amperes at 1 volt, for example. Preferably,during a practice of my method, the heat input region is heated to atemperature higher than the operating temperature of the device, toassure desired release of surbstantially all gases from the wall 10 `ofthe device, the capillary lining 12 and the working medium 13. Suchhigher temperature may be about 1600 C., requiring a power input of 2950amperes rat 1.75 volts.

The heat pipe also has a heat utilization or dissipation zone 32 whichis heated by the condensation therein of the working fiuid. This zone ofthe heat pipe includes the nipple 14, heated by the electrical currentfrom a variable transformer 34 connected to a suitable power supply, notshown. The nipple 14 is heated to a temperature higher than thetemperature to which the heat input zone 28 is heated. Such highertemperature may be about 2000 C. and is produced by a power input to theheat pipe from the transformer 34 of 275 amperes at 1.9 volts. This hightemperature prevents the condensation of the Working uid in the orificewhich would be expelled from the heat pipe at a high rate. With onlyvapor in the nipple, the rate of loss of working fluid can be controlledto a degree by the temperature of the nipple. The temperatures referredto are associated with the use of lithium as a working medium. Whereother working media having operating temperatures other than about 1400C. are used, the temperatures referred to should be modified to preservethe ratio of such temperatures to the operating temperature as indicatedin the foregoing.

The higher temperature at the nipple 14 is desirable to preventcondensation of the working medium therein, particularly in the annularorifice region defined by the wire 19 and the nipple 14. Suchcondensation would increase the outliow of working medium through theorifice to an objectionable degree.

For closing the annular orifice referred to, the output of thetransformer 34 is increased to 400 amperes at 3 volts. This softens thewall of the nipple 14 and causes it to form a meniscus that bridges theannular space between the Wire `19 and the inner surface of the nipple.When the temperature of the nipple is subsequently reduced to a valuebelow the softening point of the nipple 14, the meniscus hardens andforms a permanent seal.

During operation of the heat pipe 10, the amount of Working mediumtherein should be sufficient to lill the capillary lining 12. Thisassures maximum efficiency of the device. Therefore, in practicing mynovel method, the initial charge 13 of lithium is in suiicient quantityto permit loss of working medium through the annular orifice 16 duringthe evacuation and outgassing yof the heat pipe, and yet leave asufficient quantity of working medium in the heat pipe to fill thecapillary lining thereof after the orifice 16 has been sealed. In oneexample, the quantity of lithium as the working medium required to fillthe capillary lining 12 is 6 grams and the amount of the initial lithiumcharge 13 is 10 grams. The charge 13 therefore includes an excess of 4grams of working medium above that required for high efiiciencyoperation of the device.

My novel method provides a means 4for determining accurately when theaforementioned excess of working medium has been permitted to escapethrough the orifice 16 during the outgassing and evacuating operation.As shown in FIG. 2, this determination may be effected with the aid ofreceptacle 36 having an opening 38 positioned slightly above the orice16. Around the opening 38 is an upturned lip 39 having a function to bedescribed. The receptacle 36 is supported adjacent to one end of a lever40 fulcrumed at 42 and having a weight 44 adjacent to the other end. Apointer 46 fixed to the lever 40 is adapted to traverse an indicator 4Swhen the lever is annularly moved on fulcrum 42. The indicator hascalibrations thereon indicating the magnitude of angular deflection ofthe lever 40. The weight 44 is equal in magnitude to the sum of theweight of the receptacle 36 when empty and the weight of the excessworking medium that is permitted to be lost from the pipe 10 during itsoutgassing and evacuation.

As working medium vapor escapes from the orifice 16 during a practice`of my method, it rises into the receptacle 36 and condenses on thewalls thereof. The condensate lmay iiow to the bottom of the receptaclewhere it is prevented from escape through the opening 38 by the upturnedlip 39. The working medium so accumulated in the receptacle 36 adds tothe weight thereof.

When the total weight of the receptacle 36 and the working mediumcollected therein equals the value of the weight 44, the pointer 46moves to a position opposite a calibration on indicator 48 indicatingsuch equality. At this time, all `of the excess working medium has beenlost from the heat pipe. To prevent further loss, the transformer 34 isadjusted to provide electrical power of 400 amperes at 3 volts to theheat utilization zone 32 that is sufficient to soften the nipple 14 andt-o produce a meniscus bridging the space between it and the wire 19.The transformer 34 is then adjusted to a lower power output whichresults in a hardening of the meniscus and sealing of the device.

If the pressure of the working fiuid within the device exerts a force onthe meniscus greater than the capillary force associated with thematerial forming the meniscus, the material will be forced out of theorifice preventing a closure. If this happens it is necessary to reducethe temperature of the heat pipe until the pressure exerted on themeniscus by the working uid is less than the capillary force. To obtainthe best possible Vacuum in the heat pipe it is desirable to close theorice when the heat pipe is at its operating temperature. This is notnecessary however if a higher pressure of the impurity gases can betolerated, since the orifice can be closed in the same manner even if noother heat is applied to the heat pipe than that by the orifice heater.

It will be appreciated from the foregoing that I have provided a noveland advantageous method of outgassing, evacuating and sealing a vapordevice.

I claim:

1. Method of outgassing and evacuating a vapor device having anenvelope, said envelope including `a heat input region and a heatdissipation region and containing a vaporizable heat transfer medium,said envelope at said heat dissipation region including walls definingan orifice for venting gases from said envelope, said method comprising:

(a) evacuating said envelope,

(b) heating said heat input region to a first temperature that is atleast as high as that required for vaporizing said heat transfer medium,whereby said heat transfer medium urges said gases through said orifice,

(c) heating said heat dissipation region to a second temperature higherthan said first temperature but below a third temperature at which awall of said orifice softens, whereby that portion of said heat transfermedium passing through said orifice is preserved in the vapor state forpreventing excess loss of said medium through said orifice, and

(d) heating said heat dissipation region to said third temperature,whereby said wall of said orifice softens and closes said orifice.

2. A method according to claim 1 and wherein said softened wall of saidorifice is hardened for effecting a permanent seal of said orifice.

3. A method according to claim 1 and wherein the difference between saidfirst temperature and said second temperature is about 400 C.

4. A method according to claim 1 and wherein said rst temperature isabout 200 C. higher than the operating temperature of said vapor device.

5. A method according to claim 1 and wherein said iirst temperature isabout higher than the operating temperature of said device, said secondtemperature is about 30% higher than said operating temperature, andsaid third temperature is equal to the meniscus forming softeningtemperature of a wall defining said orifice.

6. A method according to claim 1 and wherein said heating steps areeffected by electric current losses in portions ofthe walls of saidvapor device and in the walls dening said oriiice.

7. Method of outgassing and evacuating the envelope of a vapor devicecomprising:

(a) introducing into said envelope a heat vaporizable heat transfermedium in an `amount in excess of that required for operation of saiddevice,

(b) simultaneously evacuating said enevelope and heating said medium atleast to its vaporization temperature, whereby a portion of said mediumis evacuated from said device, and

(c) stopping evacuation of said envelope when the weight of saidevacuated portion of said medium equals the weight of said excess ofsaid medium.

8. In a method of outgassing and evaculating a vapor device having anexcess of vaporizable working medium therein comprising:

(a) outgassing and evacuating gases and a portion of said working mediumfrom said device,

(b) collecting and weighing the evacuated portion of said workingmedium, and

(c) stopping the evacuation of said device when the weight of saidcollected portion of said working medium substantially equals the weightof said excess of said medium.

9. Method of sealing an evacuated device having a wall of relatively lowmelting point metal defining an elongated passageway terminating in anorifice, comprising:

(a) inserting in said passageway a wire made of a relatively highmelting point rnetal and having a diameter for nearly bridging oppositewalls of said passage- Way,

(b) heating said wall to a temperature to cause said wall t0 soften andcontact all sides of said wire while preserving said wire fromsoftening, and

(c) cooling said wall for hardening the same including the portionthereof contacting said wire, for sealing said orifice.

10. A method according to claim 9 and wherein a meniscus is formedbetween and contacting said wire and wall when said wall is heated tosaid temperature.

References Cited UNITED STATES PATENTS 1,255,979 2/ 1918 Berberich.

2,535,477 12/ 1950 Andrae 29--422 3,119,176 1/ 1964 Buesseler et al29-422 X 3,153,846 10/ 1964 Lindberg 29-422 X 3,153,847 10/ 1964Lindberg 2.9-400 THOMAS H. EAGER, Primary Examiner.

U.S. C1. X.R.

1. METHOD OF OUTGASSING AND EVACUATING A VAPOR DEVICE HAVING ANENVELOPE, SAID ENVELOPE INCLUDING A HEAT INPUT REGION AND A HEATDISSIPATION REGION AND CONTAINING A VAPORIZABLE HEAT TRANSFER MEDIUM,SAID EVELOPE AT SAID HEAT DISSIPATION REGION INCLUDING WALLS DEFINING ANORIFICE FOR VENTING GASES FROM SAID ENVELOPE, SAID METHOD COMPRISING:(A) EVACUATING SAID ENVELOPE, (B) HEATING SAID INPUT REGION TO A FIRSTTEMPERATURE THAT IS AT LEAST AS HIGH AS THAT REQUIRED FOR VAPORIZINGSAID HEAT TRANSFER MEDIUM, WHEREBY SAID HEAT TRANSFER MEDIUM URGES SAIDGASES THROUGH SAID ORIFICE, (C) HEATING SAID HEAT DISSIPATION REGION TOA SECOND TEMPERATURE HIGHER THAN SAID FIRST TEMPERATURE BUT BELOW ATHIRD TEMPERATURE AT WHICH A WALL OF SAID ORIFICE SOFTENS, WHEREBY THATPORTION OF SAID HEAT TRANSFER MEDIUM PASSING THROUGH SAID ORIFICE ISPRESERVED IN THE VAPOR STATE FOR PREVENTING EXCESS LOSS OF SAID MEDIUMTHROUGH SAID ORIFICE, AND (D) HEATING SAID HEAT DISSIPATION REGION TOSAID THIRD TEMPERATURE, WHEREBY SAID WALL OF SAID ORIFICE SOFTENS ANDCLOSES SAID ORIFICE.